It has been for many years common practice in the art of geophysical exploration for oil, gas and other minerals to perform seismic exploration of the earth's subterranean structure. From knowledge of the shapes of various layers of differing types of rocks in the earth's crust, experienced geophysicists can deduce the possible presence of various valuable minerals such as oil and gas. Seismic techniques generally involve the generation of a source of acoustic energy such as a blast of dynamite, the dropping of a heavy weight on the earth's surface or imparting of a mechanical vibration to the earth, the so-called "Vibroseis" technique.
However generated, the acoustic energy travels downwardly through the earth and is reflected at the interfaces between differing layers of rock and returns upwardly to the earth's surface. The return of the waves of acoustic energy is detected by one or more geophones placed on the earth's surface. The time taken for the wave to travel downwardly, be reflected, and return upwardly, is measured and the time is proportional to the depth of the interface from which the wave was reflected between successive layers of rock beneath the earth's surface. Additional time measurements are then made with the source of acoustic energy and the detector spaced a distance from the first; comparison of the times taken by the first and second waves yields an indication of the change in the depth of the interface between the rock layers as the source and detectors move from one location to the next. If the outputs of the detectors are properly processed and are graphed in accordance with the relative positions of source and detector, a representation of a cross-section of the earth results, on which the interfaces between rock layers appear as deflections on the individual output lies, or "traces".
Much seismic exploration has been carried out so as to provide a record indicative of a cross-section of the earth taken along a line of exploration. That is, the exploration has been generally linear. See U.S. Pat. No. 3,240,286 to Musgrave. However, it has been increasingly desirable to provide a more detailed picture of the subsurface of the earth; hence three-dimensional techniques have more recently been developed. See for example U.S. Pat. No. 4,403,312 to Thomason. In the Thomason technique, a plurality of arrays of detectors broaden the lines of exploration to yield a three-dimensional picture of the subsurface data.